In electronic communication systems two devices generally become synchronized in order for the devices to successfully communicate information (data) with each other. In communication systems that are in common use at this time, synchronism must occur at a symbol clock rate as well as at higher levels, such as word and/or frame clock rates, before data is communicated.
Synchronizing preambles are typically used to attain the synchronization required. The preambles used in current wide area radio communication systems are kept as short as practical in order to attain reliable synchronism at a designed maximum separation distance between a user device and a network station, thereby providing a high data throughput in the system. In certain cellular communication systems, when a user device is within range of a network station of a cell, and the user device is ready to establish contact with the network station for the purpose of sending a data message to the network station, the user device sends a synchronizing preamble to the network station. The synchronizing preamble in 3GPP LTE (3rd Generation Partnership Project, Long-Term Evolution) communication systems comprises one of a quantity of different synchronizing sequences of data symbols. The data symbols represent complex values. The quantity of different synchronizing preambles has to be large enough to achieve an acceptably low probability that a network station receives the same synchronizing preamble from two user devices that are operating near the network station. The plurality of synchronizing sequences are derived from a much smaller plurality of carefully chosen “root” or “base” symbol sequences that have been selected because they have characteristics that optimize the synchronization process. The characteristics are not affected by cyclical shifting of the base sequence symbols.
The quantity of different sequences are derived by cyclically shifting the symbols of the base sequences by a multiple of a defined quantity of the symbols. The duration of the defined quantity of the symbols is approximately equal to the propagation delay that occurs at a maximum range at which the synchronizing preamble will be reliably received under normal circumstances. When the user device transmits the synchronizing preamble from beyond the maximum range, it will be appreciated that the signal strength of the synchronizing preamble may be sufficient to allow enough symbols to be correctly received so that the network station can achieve synchronization. This circumstance arises because of the well known vagaries of radio wave propagation. Under this circumstance of being beyond the maximum range and yet having sufficient signal strength to attain synchronism, the propagation delay will likely cause the network station to recover the synchronizing preamble as if it were a synchronizing preamble that was derived from the base sequence with one less multiple of the defined quantity of symbols than was used to actually generate the synchronizing sequence that was transmitted, and the synchronization of the associated data message may fail even though there is sufficient signal strength for the synchronization to succeed.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.